In copiers for copying an original, printers for outputting data from computers including personal computers and printers of facsimile receivers, an electrophotographic method or electrostatic recording method has conventionally been widely employed as a technique for obtaining a copied image or a recorded image. Typical examples of the copiers and printers using the electrophotographic method or the electrostatic recording method include electrophotographic copiers, laser beam printers, printers using liquid crystal array and electrostatic printers. In the electrophotographic method or the electrostatic recording method, an electrostatic latent image (electrostatic charge image) is formed by various means on an electrostatic charge image carrier such as an electrophotographic photoreceptor or an electrostatic recording body, this electrostatic latent image is developed by a developer, the resulting toner image is, if necessary, transferred to a body onto which the toner image is to be transferred, and the toner image is fixed by heating, pressing or heat-pressing or by using a solvent vapor to obtain a final toner image, whereas the toner not having been transferred but remaining on the electrostatic charge image carrier is removed by a cleaning means. A plurality of copies or recorded products can be obtained in sequence by repeating the above-mentioned steps.
As a method for developing the above-mentioned electrostatic latent image, there are known a method of using a liquid developer wherein fine toner particles are dispersed in an electrically insulating liquid (wet developing method); a method of using a powdery toner, wherein a colorant and, if necessary, a magnetic substance are dispersed in a binder resin, together with carrier particles and a method of using a magnetic toner, wherein a magnetic substance is dispersed in a binder resin, without using carrier particles (the latter two being dry developing methods). Of these methods, the dry developing method using a powdery toner or a magnetic toner has been mainly employed in recent years.
Recently, the electrophotographic copiers and laser beam printers have been made smaller in size and have been adapted to personal use and, at the same time, have been required to be higher in printing speed and spend less energy. Therefore, various improvements have been tried on these apparatuses to form highly reliable and high-quality images at a high speed and with a low energy for a long period of time through a mechanism as simple as possible. In addition to the improvements of such apparatuses, various improvements of the toner to be used upon development have also been tried.
For example, as an apparatus for fixing a toner image, there have been widely employed a heat- and pressure-applying fixing apparatus using a heating roller and a heat- and pressure-applying fixing apparatus wherein a cylindrical or long heat-resistant film, so-called fixing belt, is used, the fixing belt is placed between a heating body and a transfer sheet, the heating body and the face of transfer sheet to be developed face each other, and the transfer sheet is conveyed with applying pressure from the back side thereof by means of a pressure-applying roller to conduct fixing by applying heat and pressure. In the fixing method using these heat-fixing apparatuses, the heating roller or the fixing belt directly contacts with the toner image upon fixing, and hence heat can be conducted to the toner with a good efficiency and the toner can be molten rapidly and smoothly with a low energy. On the other hand, however, since the molten toner directly contacts with the heating roller or the fixing belt upon fixing, there is involved a problem that part of the molten toner is transferred and adheres to the surface of the heating roller or the fixing belt and, when the heating roller or the fixing belt again contacts with a body onto which the toner image is to be transferred such as paper, this transferred and adhering toner is re-transferred onto the body onto which the toner image is to be transferred or that, in the case where no such body onto which the toner image is to be transferred exists, the toner having been transferred to the heating roller or the like is transferred to the pressure-applying roller and, when a next body onto which the toner image is to be transferred passes through the fixing apparatus, the back surface of the body is stained by the toner adhering on the pressure-applying roller, that is, a problem of so-called offset phenomenon to stain the body onto which the toner image is to be transferred.
In order to prevent such offset phenomenon of toner, it has popularly been conducted to form the surface of the heating roller by a parting material such as silicone rubber or fluorine-containing resin and apply on the surface a liquid having a good parting property such as a silicone oil to cover the surface of the heating roller with a parting liquid film layer. This technique can almost completely prevent generation of the offset phenomenon. In the method, however, an application apparatus far applying the parting liquid is required and, in addition, there arises a problem that the silicone oil is evaporated by heat to stain the inside of the copier or printer. Also, to provide such application apparatus for applying the parting liquid is inconsistent with size reduction of the copier or printer. Therefore, it has been proposed that, in place of applying a parting liquid with the application apparatus, a parting substance is incorporated in the toner itself and, by heating upon fixing, the parting substance is molten to thereby feed a parting liquid from the toner and prevent the offset phenomenon. As such parting substance, JP-B-52-3304 and JP-A-60-252360 illustrate many waxes such as low molecular weight polyethylene, low molecular weight polypropylene, hydrocarbon-based wax, natural wax and modified waxes obtained by modifying them.
In addition, it has been attempted to prevent generation of the offset phenomenon by improving the characteristics of the binder resin of the electrostatic charge image-developing toner. As examples of such binder resin having excellent offset-resisting properties, there are known cross-linked polyester resins obtained by reacting an etherified diphenol, a dicarboxylic acid component and a monomer component having three or more valences to form a cross-linked structure (JP-A-1-155362), and cross-linked polyester resins obtained by reacting an etherified diphenol, and a dicarboxylic acid component including a specific dicarboxylic acid and a tri- or more-valent monomer component including trimellitic anhydride to form a cross-linked structure (JP-A-57-109825) . However, all of these are not necessarily good in low temperature fixing property.
On the other hand, from the standpoint of improving the low temperature fixing property of a toner, it is effective to decrease the softening temperature (Tm) of a toner binder resin. In general, however, it is known that decreasing of Tm simultaneously causes decreasing of the glass transition temperature (Tg) of the toner and, therefore, the toner is liable to form agglomeration during storage, called “toner blocking”, or cause the offset phenomenon of the toner upon fixing. This is one of the reasons why the fixing temperature cannot be decreased as desired. As a method for obtaining a satisfactory low temperature fixing property and a satisfactory anti-blocking or anti-offset property at the same time, there has been proposed a method of using a polyester-based resin showing a comparatively low fixing temperature even when Tm or Tg is high (JP-A-56-1952) . However, this method fails to provide a sufficiently satisfactory low temperature fixing property and a sufficiently satisfactory anti-blocking property or anti-offset property at the same time. It is also known to use, as an alcohol component of the polyester resin, both an alkylene glycol and an etherified diphenol in combination (e.g., JP-A-1-267661, JP-A-1-155360, etc.). However, this method shows only an insufficient pulverizing property or has a low Tg, and hence the resulting toner fails to show a sufficiently satisfactory anti-blocking property. In addition to these methods, there have been made many proposals as to polyester resins for use in toner binder, such as non-linear, cross-linked polyester resin wherein the alcohol component comprises bivalent alcohol and the acid component comprises rosin, unsaturated dicarboxylic acid and other dicarboxylic acid (JP-A-4-70765), polyester resin wherein a specific alcohol component or a specific acid component is used (e.g., JP-A-6-27728, JP-A-9-278872, JP-A-10-268558, etc.), an example of using a block polymer (JP-A-2001-324832) and an example of using an amorphous polyester and a crystalline polyester in combination (JP-A-2002-84866) Thus, it has been continued to develop a resin for toner which can provide a toner simultaneously satisfying requirements for anti-offset property, low temperature fixing property, sharply melting property, anti-blocking property, charging property, pulverizing property and transparency.
As is described above, it has conventionally been attempted to produce a toner for developing an electrostatic charge image having good properties using a polyester resin as a binder resin for the toner. However, it has conventionally popularly been conducted to use bisphenol A or its derivative as an alcohol component in obtaining a polyester binder resin for a toner having good characteristic properties. In recent years, however, it has become apparent that, in view of environmental hormone use of bisphenol A is not necessary favorable. Therefore, it has been desired to develop a polyester resin for toner, which can provide a toner excellent in characteristics such as anti-offset property, low temperature fixing property, sharply melting property, anti-blocking property, charging property, pulverizing property and transparency, and can form an excellent developed image over a long period of time, as is the same with the conventional polyester resins.
Further, production cost of a toner has recently been regarded as important, and an inexpensive binder resin for toner has been demanded. However, conventional toner binders have not fully met such requirements.
Also, in view of saving resources, there has been demanded a toner for developing an electrostatic charge image which can form an image having an image density as high as with conventional toners even when a developed image has a smaller amount of toner.
With such circumstances in mind, an object of the present invention is to provide, without using bisphenol A or the derivative thereof as an alcohol component, a polyester resin for a toner which can show excellent anti-offset property in the fixing step according to the heat roller fixing system or the fixing belt system, and which provides a toner excellent in characteristics such as low temperature fixing property, sharply melting property, anti-blocking property, charging characteristics, pulverizing property and transparency and being capable of forming an excellent developed image over a long period of time.
Another object of the invention is to provide a toner for developing an electrostatic charge image, which can show excellent anti-offset property in the fixing step according to the heat roller fixing system or the fixing belt system, and which provides a toner excellent in characteristics such as low temperature fixing property, sharply melting property, anti-blocking property, charging characteristics, pulverizing property and transparency and being capable of forming an excellent developed image over a long period of time, by using as a binder resin a polyester resin produced without using bisphenol A or the derivative thereof as an alcohol component.
A further object of the invention is to provide an inexpensive polyester resin for toner, which has excellent characteristic properties as a binder resin for toner, and a toner for developing an electrostatic charge image using the polyester resin for toner as a binder resin.
Still further object of the invention is to provide a toner for developing an electrostatic charge image, which can form an image of the same density as with conventional toners even when a developed image has a smaller amount of toner.
Yet further object of the invention is to provide a method for forming an image using a heating roller or a fixing belt, whereby a good fixed image can be formed without offset.